System and method for inferring schematic and topological properties of an electrical distribution grid

ABSTRACT

A system and method for inferring schematic and topological properties of an electrical distribution grid is provided. The system may include Remote Hubs, Subordinate Remotes, a Substation Receiver, and an associated Computing Platform and Concentrator. At least one intelligent edge transmitter, called a Remote Hub Edge Transmitter, may transmit messages on the electrical distribution grid by injecting a modulated current into a power main that supplies an electric meter. The Subordinate Remotes, Remote Hubs, the Substation Receiver, and the associated Computing Platform and Concentrator may contain processing units which execute stored instructions allowing each node in the network to implement methods for organizing the on-grid network and transmitting and receiving messages on the network. The Substation Receiver, Computing Platform, and Concentrator may detect and infer schematic grid location attributes of the network and publish the detected and inferred attributes to other application systems including geospatial information systems.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 15/177,930, filed on Jun. 9, 2016, entitled “SYSTEM AND METHODFOR INFERRING SCHEMATIC AND TOPOLOGICAL PROPERTIES OF AN ELECTRICALDISTRIBUTION GRID,” which claims priority to U.S. patent applicationSer. No. 13/871,944, filed on Apr. 26, 2013, entitled “SYSTEM AND METHODFOR INFERRING SCHEMATIC AND TOPOLOGICAL PROPERTIES OF AN ELECTRICALDISTRIBUTION GRID,” which claims the benefit of U.S. ProvisionalApplication No. 61/779,222, filed on Mar. 13, 2013, entitled “SYSTEM ANDMETHOD FOR INFERRING SCHEMATIC AND TOPOLOGICAL PROPERTIES OF ANELECTRICAL DISTRIBUTION GRID” and U.S. Provisional Application No.61/766,551, filed on Feb. 19, 2013, entitled “SYSTEM AND METHOD FORINFERRING SCHEMATIC AND TOPOLOGICAL PROPERTIES OF AN ELECTRICALDISTRIBUTION GRID,” the disclosures of each of which are herebyincorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention is directed toward employing the electricaldistribution grid as a short and long-range transmission medium anddata-bearing network, and further toward the use of signals and messageson the network for the purpose of inferring schematic and topologicalproperties of the distribution grid, which vary over time.

BACKGROUND OF THE INVENTION

The power grid is generally considered to be composed of two logicalregions, the Transmission Grid(s) and the Distribution Grid(s). TheTransmission Grid originates at large generation points such ashydroelectric dams, nuclear reactors, wind farms, and coal-fired orgas-fired power plants. Power from the generation point is transmittedas high-voltage alternating current (AC) over a loosely connectednetwork of long, high-voltage lines to points where demand for powerexists, such as factories, farms, and population centers. At the edgesof the Transmission Grid there is a collection of DistributionSubstations. Distribution Substations contain one or more SubstationTransformers, which step down the voltage from high transmission linelevels (typically 130 kV to 700 kV) to the medium voltage levels(typically from 4 kV to about 35 kV) at which power is distributed toconsumers within a distribution service area. At the edge of theDistribution Grid are a number of Service Transformers, which transformthe medium voltage of the distribution grid to the low voltages (in theUS, typically 120V, 208V, 240V, 277V, or 480V). Other voltages inaddition to some of these can be used elsewhere in the world. In somecases, a tier of one or more transformers, called step-downtransformers, lying schematically between the Substation Transformersand the Service Transformers, create intermediate voltage reductionsbetween the Substation and the Service Transformers. Each ServiceTransformer powers one or more metered loads. A load can be a dwelling,a commercial or industrial building, an element of municipalinfrastructure such as a series of street lamps, or agriculturalapparatus such as irrigation systems. A typical distribution gridincludes other elements used to balance and regulate the flow of power.Examples of such elements are capacitor banks, voltage regulators,switches, and reclosers. FIG. 1 illustrates a typical segment of thepower grid.

Distribution grids have been designed and deployed in a variety oftopological configurations. In the United States, distribution gridtypes are typically characterized as radial, loop, or networked. Otheremerging cases are the campus grid and the microgrid. Additionaltopologies, not described, are used elsewhere in the world.

FIG. 2a is a topological schematic of a typical radial grid. In a radialgrid, a substation has one or more substation transformers. Eachsubstation transformer has one or more substation busses. One or morethree-phase feeders “radiate” outward from each substation bus, withsingle-phase, double-phase, or three-phase lateral lines branching offfrom the feeders, and tap-off points (or simply “taps”) in turnbranching from the laterals. Radial grids are inexpensive to design andbuild because they are simple, but they are most vulnerable to outagesbecause they lack redundant power paths, so that any break causes atleast one load to lose power.

FIG. 2b is a topological schematic of a typical loop distribution grid.In a loop grid, each end of select feeders is attached to a power sourcesuch as a bus of a substation transformer. If the loop is undamaged,then power is available at all loads if either substation transformer isoperational. If there is a break in the loop, then power is available atall loads assuming that both transformers are operational. In normalcircumstances, a system of switches is used to ensure that only onesubstation transformer at a time is delivering power to each segment ofthe grid.

FIG. 2c is a topological schematic of a typical networked grid. Thistopology has maximum redundancy. In addition to employing multiple powersources, all the service transformers are linked to one another on thesecondary side in a mesh arrangement. Multiple breaks in connectivityare required to cause a power outage at any point. Networked grids aremost expensive to build and maintain, and are typically used in majorurban areas such as Manhattan or Washington, D.C. where high-value,high-criticality loads are concentrated together.

FIG. 2d shows a microgrid or campus network. Microgrids are nottraditional in electrical distribution technology, but are emerging as aresponse to increased focus on energy conservation and on distributedgeneration of energy from renewable sources. Many variations arepossible. This type of grid is typically attached to, but severablefrom, a wider distribution grid, and may contain its own power sourcessuch as windmills, solar panels, or rechargeable storage batteries aswell as loads. The entire network may employ low-voltage lines.

A distribution substation receives high-voltage power from thetransmission grid into one or more large power transformers. Adistribution transformer may incorporate a type of regulator called aload-tap changer, which alters the voltage the transformer delivers to apower distribution bus (the substation bus) by including or excludingsome turns of the secondary winding circuit of the transformer, therebychanging the ratio of input to output voltage. One or more feedersdepend from the substation bus. If too many feeders are required,additional transformers and busses are used.

In order to monitor and control the components of the grid, currenttransformers (CTs) or other current sensors such as Hall-effect sensorsare attached to power-bearing conductors within the substation. The CTsoutput a low current on a looped conductor which is accuratelyproportional to the current delivered at the high voltage conductorbeing monitored. These low-current outputs are suitable for connectingto data acquisition subsystems associated with Supervisory Control andData Acquisition (SCADA) systems in the substation, Primary monitoringCTs are designed and built into the substation, because changing oradding CTs to the high-voltage components is impossible or dangerouswhile current is flowing. On the other hand, additional CTs may besafely added to the low-current SCADA loops as needed without impactingpower delivery.

In addition to the power lines themselves, the distribution gridcontains numerous other devices intended to regulate, isolate,stabilize, and divert the flow of power. These devices include switches,reclosers, capacitor banks (usually for power factor correction), andsecondary voltage regulators. All these devices affect the behavior ofthe distribution grid when considered as a data-bearing network, as dothe various loads and secondary power sources on the grid. Devices thathave abrupt state changes will introduce impulse noise on the grid, ascan loads turning on and off. Some devices, such as transformers andcapacitor banks, filter and attenuate signals at certain frequencies.

Other than the wires connecting a consumer load and the associated meterto a service transformer, the service transformer is the outermostelement of the distribution grid before the power is actually deliveredto a consumer. The meter is attached at the point where the power fromthe service transformer is delivered to the consumer. Servicetransformers can be three-phase, dual-phase, or single phase, as canmeters.

Traditionally, reading meters was one of the largest operational costsincurred by electrical utilities. Original electric meters were analogdevices with an optical read-out that had to be manually examinedmonthly to drive the utility billing process. Beginning in the 1970s,mechanisms for digitizing meter data and automating its collection beganto be deployed. These mechanisms evolved from walk-by or drive-bysystems where the meter would broadcast its current reading using ashort-range radio signal, which was received by a device carried by themeter reader. These early systems were known as Automated Meter Readingsystems or AMRs. Later, a variety of purpose-built data collectionnetworks, employing a combination of short-range RF repeaters in a meshconfiguration with collection points equipped with broadband backhaulmeans for transporting aggregated readings began to be deployed.

These networks were capable of two-way communication between the“metering head-end” at a utility service center and the meters at theedge of this data collection network, which is generally called theAdvanced Metering Infrastructure or AMI. AMIs can collect and storereadings frequently, typically as often as every 15 minutes, and canreport them nearly that often. They can read any meter on demandprovided that this feature is used sparingly, and can connect ordisconnect any meter on demand as well. AMI meters can pass signals toconsumer devices for the purpose of energy conservation, demandmanagement, and variable-rate billing. Because the AMI network isseparate from the power distribution grid, AMI meters are neither awareof nor sensitive to changes in the grid topology or certain conditionson the grid. Nonetheless, the introduction of AMI is generallyconsidered to be the beginning of the Smart Grid.

Many characteristics of the electrical distribution infrastructure havelimited the success of efforts to use the grid itself as acommunications medium. First, the grid is a noisy environment. Asalready noted, state changes in loads on the grid as well as control andregulation artifacts on the grid itself cause impulse noise on the powerline. Normal operation of loads like electrical motors, simplevariations in the overall load, and ambient RF noise (chiefly fromlightening and other weather-related causes) add up to significantGaussian noise. The measured noise floor at a typical substation in theUnited States sits at about 80-90 dB below the maximum amplitude of the60 Hz fundamental. The complex impedance of the grid varies across boththe frequency and time domains. This may lead to loss of signal at areceiver sited at a higher voltage point on the grid when impedanceincreases, or alternately force the transmitter to use more energy thanwould be necessary on the average. Capacitor banks sited at points alongthe grid for the purpose of optimizing the power factor can cause signalattenuation. Most significantly, transformers act as low-pass filters,dramatically attenuating signals above a certain frequency. Thethreshold frequency is not the same on every distribution grid, becausedifferent arrangements and types of transformers are employed andbecause the transformers themselves are not deliberately tuned to filterat a specified frequency. All these variables impact the frequencyresponse of the medium.

Additionally, injecting modulated current signals on the grid may causeinterference between the injected signals themselves. One problematicphenomenon is crosstalk, where a signal injected on one power line isdetectable on another line. When crosstalk occurs on two or more phasesof the same feeder, it can be caused by inductive and capacitivecoupling, as the phase lines run alongside one another for most of thelength of the feeder. Crosstalk may also be due to multiple phasewindings on the same transformer core. Feeder-to-feeder crosstalk hasalso been measured, and may be caused by reflection of the injectedsignal off the power bus at the substation. Given the complexity,diversity, and age of the distribution grids in the United States andthe world, less is known about these phenomena than might be expected.

Finally, using the distribution grid as a communications medium oftenhas side effects which interfere with the primary purpose of the grid,which of course is delivering clean, reliable power to consumers. Ifdevices under power resonate with an injected current, a phenomenoncalled flicker results. LED, CFL, incandescent and fluorescent lightingvisibly flickers in response to certain frequencies. This is annoyingand sometimes dangerous, as visual flicker has been demonstrated tocause both seizures and vertigo. Other types of devices, such as fansand speakers, also resonate at certain frequencies, causing an audiblehum. ANSI/IEEE standard 519 requires any device (whether intended as acommunication device or not) that injects current on the grid to avoiddoing so at certain frequencies and amplitudes to avoid causing flicker.Specifically, ANSI/IEEE standard 519 requires that no noise be added tothe odd harmonics of the fundamental at or below the eleventh harmonic.

Despite the many engineering difficulties inherent in using the powergrid as a communications medium, it has remained attractive toelectrical utilities because the utility already owns theinfrastructure, and it is present at all the points where the utilityneeds to collect data. Further, the regulatory and cost structure ofpublicly owned utilities (POUs) strongly favors them using owned assets(which can be profitably purchased and maintained via service rateincreases) as opposed to paying operating expenses to a third-partycommunications provider such as a telephone or cable provider.

High-frequency transmissions (above 1 MHz) are attractive becausetheoretically high data rates can be achieved. Such schemes, called BPLfor Broadband over Power Lines, offer a potential theoretical bandwidthsufficient to deliver Internet access to consumers via a gateway locatedin their electrical meter. In the early years of the twenty-firstcentury, the Federal Communications Commission (FCC) in the U.S.actively promoted the concept of “Access BPL” as a means of deliveringhigh-speed Internet access to rural American families. Long-rangetransmission of BPL signals, however, is impractical and expensive,because every transformer between the transmitter and the receiver mustbe fitted with a bypass or repeater mechanism, or the low-pass filteringcharacteristics of the transformer will block the signal. In the UnitedStates, where the number of consumers per service transformer tends tobe very small—in rural areas often only one—the cost to implement BPLbecomes prohibitive. Additionally, RE interference caused by BPLtransmission has created opposition from aviation, commercial radio,amateur radio, and other sectors. The FCC has attempted to be supportiveof BPL technology, but new compromise rules requiring BPL installationsto be capable of notching out (avoiding) frequencies where interferenceis reported have increased the complexity of managing a BPL service.Several attempts at deploying BPL consumer services have been abandoned.

Under the umbrella name Power Line Communication or PLC, somemedium-frequency power line protocols have been used with success forSmart Grid applications, especially in Europe (and other locales withEuropean-style grid architectures), where the number of consumers perservice transformer is much larger than in the United States. The twomost commonly used medium-frequency PLC initiatives are PRIME and C3,both promoted by commercial alliances based in Europe. PRIME usesorthogonal frequency-division multiplexing (OFDM) at the physical layer,with 512 differential phase-shift keyed channels (DPSK). PRIME achievesdata rates as high as 128.6 kbps, but is most reliable at 21.4 kbps. Itsfrequency range is 42-89 kHz. G3 uses a similar physical-layercombination of OFDM and DPSK, offering 256 channels between 35 and 91kHz with a data rate of 33.4 kbps. Both G3 and PRIME are still sharplyattenuated by transformers, though in most cases a receiver located onthe medium-voltage side of a service transformer can successfully readmeter transmissions from low-voltage sites served by that transformer,provided that the receiver is sited close enough to the servicetransformer. For these reasons, Smart Grid technologies based on theseprotocols are common in Europe and Asia. PLC protocols are alsowell-adapted to short-range power-line applications such as arbitratingthe charging of electric vehicles.

At the other end of the spectrum are ultra-low frequency systems,chiefly used for control systems because they have little data-bearingcapacity. Audio Frequency Ripple Control (AFRC) systems are used mostlyin rural areas for load management: to turn off high-consumption devicessuch as electric heaters and air conditioners during peak load times, orto control use of other constrained resources, such as automated farmirrigation systems. An AFRC transmitter sits on the high-voltage side ofa substation or transmission transformer and may service multiplesubstations. AFRC data rates vary from 2 to 10 bits per second, and themaximum message length is about 100 bits. After such a transmission, thetransmitter requires a long idle period before it can transmit again,with a maximum duty cycle on the order of 10%. AMC systems cause obviousflicker, but not at a dangerous frequency. Because they are typicallyused in areas of low population density and transmissions areinfrequent, the side effects are tolerated. AFRC is a broadcasttechnology operable from high voltage to low voltage and thus cannot beused for collecting meter data or other data about edge conditions,because that requires transmitting from low voltage to higher voltage.

Aclara®'s TWACS® technology operates by injecting pulses onto the powerline when the fundamental power carrier crosses the zero point—twice per50 Hz or 60 Hz cycle. This method operates either from substation toedge or edge to substation, and uses a polling protocol to avoid havingone edge transmission interfere with another. It is slow because it istied to the fundamental, and because of the polling architecture. It hasbeen criticized by consumer groups for the amount of impulse andbroadband noise it introduces onto the grid.

Landis±Gyr employs a low-cost, low-frequency edge transmitter originallydeveloped by Hunt technologies, intended to operate in conjunction withAFRC to provide two-way communication over long distances on the grid.The data transmission method using this transmitter is cheap andreliable, but limited. It induces sympathetic current oscillations byconnecting variable impedance to the power line. The data rate is lowbecause the transmitter is dependent on a voltage relative to the powercarrier, so that only a few pulses can be injected per 50 Hz or 60 Hzcycle. To achieve enough redundancy for detection at the receiver, thesame signal must be repeated for several cycles, resulting in a datarate measurable in cycles per bit rather than bits per cycle. The methodis also very noisy, in that each pulse resonates across a broadfrequency band.

Despite their limitations, low-frequency systems such as those fromAclara and Landis+Gyr have achieved market penetration in rural areaswhere wireless systems are cost-prohibitive.

The problems with, and limitations of, the high, medium, andlow-frequency PLC methods as discussed above have led in the 21^(st)century to rapid development of custom built wireless networks for AMIdata collection in the U.S. High-frequency on-grid methods have provento be too expensive, not sufficiently reliable, and too fraught witherror and uncertainty to be commercially viable. Low-frequency methodscan be implemented with low-cost edge-to-substation transmitters, butthese lack the data-bearing capacity required by modern AMI, and on-gridlow-frequency substation-to-edge transmitters like AFRC are large,expensive, and have undesirable side effects which limit their use inurban settings. One possible option would be to use high-frequencysubstation-to-edge transmitters in conjunction with low-frequencyedge-to-substation transmitters. However, in the U.S. market forces haveled to the rapid penetration of wireless AMI systems, especially inurban and suburban areas.

Cost constraints and availability of unregulated spectrum have dictatedthe use of mesh architectures at the edge of the AMI networks, withneighborhood concentrators that collect data from the meters and usetraditional infrastructure (fiber or cellular) for backhaul to datacenters. Mesh architecture means that although the RF transceivers usedhave individually high data rates, the edge networks are easilysaturated. Most of the available data bearing capacity in these networksis used just for reporting meter interval data, with limited capacityreserved for firmware updates and control packets for applications suchas demand management.

Two major factors limit the utility of the existing AMI infrastructures.The first is, of course, the capacity limitations of the mesh. Thesecond, and more significant, is the fact that the AMI network is notcongruent with the electrical grid. It is capable of providing littleinformation about the operational state of the grid. This is unnecessaryfor meter reading, but more sophisticated Smart Grid applications forenergy conservation, asset protection, load balancing, fault isolation,and recovery management require accurate information about the schematicrelationship of grid assets, load and conditions on the several segmentsof the grid, and the current state of bi-modal and multi-modal assets.This information, together with the geospatial locations of the sameassets, is called the Grid Map.

Utilities typically maintain two maps or models of the Grid. A PhysicalNetwork Model (PNM) aggregates the geospatial location of the assets onthe grid. PNMs, thanks to modern GPS technology, are reasonably accuratewith respect to point assets such as substations, capacitor banks,transformers, and even individual meters. Inaccuracies stem from failureto update the maps when repairs or changes are made. For example, aservice transformer may move from one side of a street to the other as aresult of street widening. Longitudinal assets, especially buriedcables, are less well represented in the PNM. The PNM can containas-designed data, but since in many places the cable was laid beforeglobal positioning technology had matured, the designs were based onground-level survey, and the original maps may or may not have beenupdated to reflect changes. Subsequent surface changes complicate theproblem of verifying the geographic path taken by medium-voltagedistribution lines.

The second model is the Logical Network Model, or LNM. LNMs describe howgrid components are connected, without reference to their geospatiallocation. The LNM changes frequently. During the course of repairs, theway transformers attach to taps and laterals, and meters attach totransformers, may be altered. Such changes affect both the LNM and thePNM. In many utilities, such changes are recorded manually by fieldagents. The manual reports may or may not be updated in the LNM and PNM,and when updates are made the time lag between maintenance occurring andits being recorded is variable. Additionally, many grid components,especially regulators, switches and reclosers, change stateautomatically. Unless these components are instrumented withcommunications back to a data center rather than simply being subject tolocal control systems, such dynamic changes are not reflected in theLNM. They do, however, affect the power path, the load and environmentalstress on other components of the distribution grid, and the servicelevel to consumers.

Examples of significant but not reliably known aspects of the (actual)Grid Map are the feeder and phase by which each meter is currentlypowered, the relative load on each phase of each feeder, especially onsubordinate branches (laterals) of the grid, the actual voltage suppliedto each meter, the power factor along the edges of the grid, whether allthe power drawn at a transformer is metered, and the state of switchsets, especially after a weather event that has caused outages. If thisinformation were reliably known, utilities could conserve energy, muchof the savings from which would pass on to consumers, save maintenancecosts, prolong the life of equipment in the field, improve theefficiency and life of utility and consumer equipment, avoid outages,and reduce recovery times after unavoidable outages.

The problem of automated, dynamic grid mapping is not solved by wirelessSmart Meters. Smart meters can measure and record current, voltage andpower factor (or phase angle) at the meter, but because they havelimitations on how much data they can store and how much data capacityis available for transmission, utilities may choose not to program themeters to report these data. The other data elements described cannot bedetected by most modem AMI systems. U.S. Pat. No. 7,948,255 to Coolidge,et al. discloses instruments for phase detection. However, theinstruments in Coolidge are intended to be used by field engineersrather than incorporated into the Smart Grid.

The consensus among utilities is that the volatility of the LAM is suchthat using field engineers to measure and monitor changing attributes ofthe grid map is not a cost effective or workable solution. For example,conservation voltage regulation efforts were undertaken in the 1990sbased on static measurements, and subsequently abandoned because themeasurements became outdated too quickly. Today, utilities habituallyoversupply consumers, delivering an average effective voltage of 122 vACto a 15 or 20 amp-rated circuit in a residence to ensure thatfluctuations in load, power losses in the home wiring, etc. do notresult in some consumers' service falling below 110 vAC effective atindividual outlets inside the building, which is generally the optimumfor home appliances and the like. The goal of a well-instrumentedfine-grained conservation voltage regulation system might be to reducethe typical effective voltage at a single-phase meter to 114 vAC asmeasured from one leg of the typical 240 vAC service to neutral. 114 vACeffective at the meter is as low as it is reasonable to go withoutrisking under-powering some outlets in the building, (i.e. not less than110 vAC at any outlet) due to additional losses which are typical insidethe home or office.

Since electrical devices consume more energy when powered at the highend of their rated range, this practice of over-delivering impactsconsumers' electric bills directly, as well as forcing generation-poorutilities to buy power, increasing their costs. Ultimately, the practiceresults in more fossil fuel being consumed than necessary.

Cost constraints also dictate that placing SCADA instrumentation atevery medium-voltage field asset is impractical. The “touch points” onthe distribution grid are, for better or worse, largely the meters atthe edge and the instrumentation in the substations. This dictates thattechniques for power line communication be revisited, because signalstraveling on the power line can be used both to infer and to report gridmapping information not detectable by means of wireless AMI. Theubiquitous presence of wireless AMI for reporting meter data can beconsidered as a benefit in the search for effective grid-mappingtechnology, in that it frees the limited data-bearing capacity oflow-frequency on-grid transmission methods to support grid mappingsystems instead. It is, however, needful to identify a transmissionmethod that is low cost at the edge, coexists with the AMR or AMI, anddoes not trigger any of the above-noted pitfalls of on-gridtransmission: requirements for intermediate devices such as repeatersbetween the edge and the substation; unacceptable flicker; REinterference; impulse noise; etc. Finally, the transmission must requirevery little power, because the energy expended driving the transmittersreduces the energy conservation benefits obtained.

As discussed above, some existing PLC methods have adapted radiomodulation techniques and channel access methods to the medium of theelectrical distribution grid. For example, PRIME uses FDMA with DPSK.

In addition, Code Division Multiple Access (CDMA) is a channel accessmethod most famously used in cellular telephony standards cdmaOne,WCDMA, and CDMA2000. CDMA spreads its signal across a range or band offrequencies, as do other similar technologies; hence the term broadband.Multiple access means that more than one transmitter can use the samechannel (here, a power line) without the signal from one transmitterdestructively interfering with the signal of another transmitter. ItsCDMA, each transmitter which uses the same band is assigned a distinctreference code or chip. The transmitted signal equals the exclusive OR(XOR) of the chip with the data signal. If the chips (treated as binaryvectors) are mathematically orthogonal, then the receiver can separateout the several data signals from the additive received waveform. Arequirement of standard CDMA as used in a wireless application is thatthere is a dynamic feedback loop from receiver to transmitter to ensurethat the power of the several signals received from the differenttransmitters is the same or nearly the same at the receiver. Thefeedback loop permits the transmitters to rapidly and dynamically adjusttheir transmission power to maintain the balance.

Frequency Division Multiple Access (FDMA) means that multiple channelsin a medium are created by having different transmitters use differentfrequencies (or different frequency bands). A signal injected on thepower line creates harmonic signals of different amplitudes. If thefrequency-division bands are incorrectly chosen, then the harmonics fromdifferent bands can coincide and create false signals that interferedestructively with the intended signals. The obvious means ofeliminating this effect is to place the channels far apart on thefrequency spectrum. This, however, reduces the overall data bearingcapability of the medium by “wasting” spectrum.

A third channel access method is Time Division Multiple Access, or TDMA.In TDMA, the channel is divided cyclically over time, with eachtransmitter sharing the channel assigned a specific time slot in thecycle where that transmitter uniquely has permission to transmit. TDMArequires that all the transmitters have system clocks which aresynchronized with one another within a close enough tolerance that onechannel accessor does not overlap its transmission with that of anotherchannel accessor.

SUMMARY OF THE INVENTION

The present invention includes a system comprising at least oneintelligent edge transmitter called a Remote Hub Edge Transmitter, eachsmall enough to reside inside a Smart Meter. A Smart Meter that containsa Remote Hub Edge Transmitter is called a Remote Hub GLA Smart Meter, orsimply a Remote Hub. The Remote Hub transmits by injecting a modulatedcurrent into a power main that supplies an electric meter. The systemalso includes at least one receiver sited at at least one electricaldistribution substation operable to receive transmissions from theintelligent transmitters. No additions or alterations to thedistribution grid between the Smart Meters and the substation arerequired to allow the receiver to reliably detect and decodetransmissions from the edge transmitters. The system further comprisesone Computing Platform for each substation that contains at least onereceiver, the Computing Platform having access to a conventional highspeed network such as the Internet for transmitting data acquired fromthe at least one receivers to a data center at which the received datais used by a Concentrating Computer System, or Concentrator, to updateother utility systems such as, but not limited to, the LNM and PNM. Insome microgrid deployments the Computing Platform and the Concentratormay be the same server, with the data center sited inside the servicearea of the microgrid. The system may additionally comprise Smart Metersor other devices, such as field-deployed switches and voltageregulators, which are not Remote Hubs, augmented by intelligentplatforms operable to employ short-range PLC transmissions using awell-known protocol such as G3 or PRIME to communicate with at least oneRemote Hub. Such augmented devices which are not Remote Hubs aredesignated as Subordinate Remotes, and any augmented device, withoutregard for whether it is a Subordinate Remote or a Remote Hub, may bereferred to generally as a Remote. Each Remote Hub manages only Remotespowered by the same service transformer as the Remote Hub. A short rangeon-grid network consisting of a collection of Remotes comprising atleast one Remote Hub and zero or more Subordinate Remotes is called aTransformer Area Network or TAN.

Subordinate Remotes, Remote Hubs, the Substation Receiver, and theassociated Computing Platform and Concentrator all contain storedprograms on non-volatile computer-readable memory on which are storedinstructions for operating a Grid Location Aware™ (GLA) network. TheSubordinate Remotes, Remote Hubs, the Substation Receiver, and theassociated Computing Platform and Concentrator also contain processingunits (CPUs) which execute the stored instructions allowing each node inthe network to implement methods for organizing the on-grid network andtransmitting and receiving messages on the network in order to permitother methods embodied as stored programs and executing on the at leastone Substation Receiver, Computing Platform and Concentrator to detectand infer schematic grid location attributes of the network and publishthe detected and inferred attributes to other application systemsincluding geospatial information systems maintaining the logical andphysical network model.

One method implemented by the Remote Hubs and the Substation Receiverprovides for channelizing and modulating current signals transmittedfrom the at least one Remote Hub in the service area of an electricaldistribution substation such that the signals are received at theSubstation Receiver and the Substation Receiver is able to infer theelectrical phase of the specific feeder upon which the signal wastransmitted. The signal is transmitted on a broad band of the frequencyspectrum called a channel, but the frequency bands of channels areselected so that the frequency is lower than the low-pass threshold ofthe service transformer that powers the Edge Transmitter. Severalmodulation techniques have been used in this context, includingfrequency spread modulation, Binary Phase-Shift Keying (BPSK), andQuadrature Phase-Shift Keying (QPSK). Higher-order modes of phase-shiftkeying (mPSK) may be used. However, BPSK and QPSK may be preferredembodiments along with frequency spreading, because higher-order PSKsrequire more power at the transmitter in order to achieve the samesignal strength at the receiver. According to some embodiments of themethods, an Edge Transmitter is capable of encoding at least 80 bits persecond of post-FEC (forward error correction) data in a bursttransmission at low but adequate current so that the signal is not sosignificantly attenuated by intermediate transformers, capacitors, longlines, underground wiring, and the like to prevent reception by theSubstation Receiver. In other embodiments, an Edge Transmitter may becapable of encoding at lower bit rates. Encoding at lower bit ratesimproves reliability, but limits the amount of data transmitted. Inorder to obtain the same post-FEC message success rate whiletransmitting at at least 80 bps, different modulation types may requiredifferent Forward Error Correction rates. The method requires littlepower to inject the signal, so that the signals as modulated do notradiate energy in the RF spectrum or cause flicker or hum on devices inproximity to the transmissions or exhibit any of the other undesirablecharacteristics of prior art methods of on-grid messaging. The methodworks on all the grid topologies described herein above, and can supporta sufficient number of Remote Hubs per substation transformer that eventhe largest substations can be fully covered by the resulting GridLocation Aware™ network.

The Substation Receiver may also implement a variety of methods ofsampling the ambient waveforms at a multiplicity of frequency bands onthe power lines, filtering out the high-energy harmonics of thefundamental power wave, detecting the signal on one or more of aplurality of power lines (comprising each of the three phase lines ofeach feeder emanating from each bus of a given substation transformer),inferring the phase and feeder combination on which the signal wastransmitted based upon a comparative analysis of each of the powerlines, ranking them based on the signal quality, error performance,and/or amplitude versus frequency at a multiplicity of points throughoutthe spectrum of interest. When the Substation Receiver has completelyprocessed a transmission, it packages the decoded transmission togetherwith any additional information about the message inferred by thereceiver logic, such as the phase and feeder on which the message wastransmitted, the channel on which the message was transmitted, and anindication of the parameters of the modulation method used for thattransmission. The Substation Receiver forwards the entire messagepackage to the substation Computing Platform using a normal TCP/IP-basedprotocol such as HTTP.

Another aspect of the invention is a method of identifying whichfrequency bands are the best data carriers at each substationtransformer, defining at least one data-bearing channel on the candidatefrequency bands, optionally defining a series of time slots on eachchannel in which edge devices may transmit, selecting a modulationtechnique, and, if frequency spreading is the chosen modulationtechnique, defining a set of at least one orthogonal codes or “chips”per channel to be used for modulating transmissions. The combinedchannelization model s then employed by the method to provision thecollection of GLA Smart Meters, including both Remote Hubs andSubordinate Remotes, supplied with power by a substation to assign toeach of the at least one Remote Hubs a policy describing on whichfrequency-based data-bearing channel(s) the Remote Hub may transmit, andunder what circumstances the Remote Hub must transmit. The policydescribes multiple aspects of the channels, including modulation method,frequency bands, chip selection algorithm if chips are used, and messagepreamble pattern. Frequency-based channels and chips must be assigned insuch a way that transmissions are not destructive when segments of thegrid are, for example, switched from one substation transformer toanother. The provisioning scheme anticipates and minimizes the problemof crosstalk, and provides means for logic on the Substation Receivers,the substation Computing Platforms and the Concentrator tohierarchically process the messages received from each Remote Hub anduse them to infer the state of stateful non-edge features of the grid,such as switches, reclosers, and breaks in the power lines. Otherproperties of the transmission are determined dynamically by firmwareand instrumentation on the Remote Hub. For example, the power used whentransmitting may be related to the impedance of the line as measuredimmediately prior to transmitting.

In some embodiments of the invention, a number of techniques may beemployed for managing channel quality, depending on the availability ofSubstation-to-Edge broadcast capability from adjacent networks, such asan AMI, AMR, and/or radio broadcast transmitter. Software on theSubstation Receivers and Computing Platform may monitor aspects of thechannel quality and take measures to ensure that messages from theRemote Hubs experience an acceptably high success rate. According to oneaspect of the invention, an acceptably high success rate may be ensuredby rotating the responsibilities of the several channels, except that atleast one non-structured channel is not rotated but remains dedicated toprovisioning and alerting. For example, if two data bearing channelshave been identified, and one data bearing channel demonstrates a highersuccess rate than the other, then the network may be provisioned to haveRemote Hubs alternate between transmitting on the better channel and theother channel. This reduces the overall probability of a given RemoteHub experiencing an unacceptably high message failure rate.

Other options for channel management may be to alter the definition of achannel so that the channel has a wider frequency spread, and/or usesmore FEC bits per burst. Still another option is to move a channel to adifferent place in the spectrum, either permanently, or at differenttimes of the day based on an observed cycle in impedance, impulse noise,or some other characteristic of the channel relevant to message successrate. None of these mechanisms require a fast feedback loop between theEdge Transmitters and the substations, as is the rule with somemodulation techniques such as CDMA. Rather, the apparatus at thesubstation conducts a time-duration analysis of the behavior of thenetwork, and then broadcasts new provisioning policy based on theanalysis. Many characteristics of the network may be taken into accountwhen making a policy change, such as observed patterns of crosstalk,variations in impedance, harmonic mixing, and the like. A policy changemay impact multiple substations which may be interconnected by switchingsystems or other forms of redundancy.

Yet another aspect of the invention is a method employed by the storedprograms at each of the at least one Remote Hubs to integrate theEdge-to-Substation GLA network with adjacent networks, such as the AMI(regardless of the AMI architecture) and the higher-frequency PLC basedTransformer Area Network, as well as with the native intelligence of theSmart Meter platforms themselves, In this method, the Remote Hub, whosehigh-frequency PLC protocol stack (e.g. PRIME) enables it to act as themaster node in the TAN, carries out the TAN-management activities. TANmanagement activities include, but are not limited to, polling the PLCprotocol stack to detect newly discovered Subordinate Remotes. TheRemote Hub also polls the local native Smart Meter intelligence toobtain local data such as current, voltage, and phase angle, and pollsthe reachable population of Subordinate Remotes to obtain similar datafrom the native Smart Meter intelligence at the Subordinate Remotes. TheRemote Hub stores, compresses, and/or processes the gathered dataaccording to the policies and application algorithms on the Remote Hubuntil the operable policy dictates that the gathered data and/or derivedresults of the gathered data may be transmitted to the SubstationReceiver by the Edge Transmitter module of the Remote Hub. The RemoteHub is further responsible for using its provisioned policy anddiscovered TAN configuration data to determine when it is appropriate toformat, encode, and transmit an alert message on an edge-to-substationchannel. Such messages may include pairing messages, which report thediscovery of a new Subordinate Remote, pairing alerts, which report theloss of communication with a known Subordinate Remote, other alertswhich report changes in the TAN or at meters (such as power surges,sags, and spikes), and scheduled data reports which transmit the datacollected from the native Smart Meter intelligence in the TAN to theapparatus at the substation. In some embodiments of the invention,channels are not time-slotted, and Remote Hubs may transmit onlyexception reports or computed data reports on a randomized postingschedule in which an adequate number of transmissions are performed toprovide an acceptable probability of achieving at least one successfultransmission at the desired rate.

If slotted channels and/or time-scheduled transmission policies areused, the Remote Hub may require a method of synchronizing its systemclock to a known tolerance with other Remote Hubs in the same servicearea. Each Remote Hub may poll the local meter or AMI network to obtainthe AMI network time, which the Remote Hub uses to determine whenscheduled transmissions must occur, and to obtain data blocks receivedvia the AMI which are intended for the Grid Location Aware™ intelligenceon the Remote Hub or on the Subordinate Hubs. Such data blocks mayinclude firmware updates and changes in network policy or provisioningwhich will affect the subsequent behavior of the Subordinate Remote. TheRemote Hub distributes firmware updates and policy changes to theSubordinate Remotes as necessary via the local PLC channel of the TAN.Additionally, Remote Hubs may synchronize based on a wireless broadcastsignal. If no synchronization method is available, channel access maynot be based on time slots at all. This reduces the data-bearingcapability of the network but does not impact the ability of the systemto provide grid-location data. In some embodiments, Remote Hubs and/orSubordinate Remotes may contain a Global Positioning System (GPS)receiver. The GPS signal may be used for synchronizing the Remote Hubsin addition to providing means to associate the logical network modelwith the physical network model.

In still another aspect of the invention, the Computing Platforms andthe Concentrator maintain two master data tables which can be initiallyextracted from the utility's PNM and/or LNM, or which can be entirelyaccumulated from reports from the Remote Hubs. These data tables are theInventory, which is a table of all the Remote Hubs and SubordinateRemotes which have been detected, and the Grid Map, which is a schematicrepresentation of the grid's topology and state, similar to an LNM. TheGrid Map and Inventory at substation Computing Platforms may be partial,representing only the portion of the grid accessible to the substationat least at certain times. The Grid Map and Inventory at theConcentrator generally represent the entire utility service area,although gaps in the Grid Map may exist if instrumentation of theservice area with Remote Hubs and Subordinate Remotes is incomplete.When the Computing Platform at a substation receives any message from aSubordinate Remote, it compares the data in the message and the messageenhancements inferred by the Substation Receiver with the data in theInventory and Grid Map. The logic and policy on the Computing Platformare used to determine if the local copy of the Grid Map and inventoryneed to be updated, and whether the update must be sent on to theConcentrator to update the master Grid Map and Inventory. If the policyin effect at the Computing Platform so dictates, the data collected fromthe edge is also forwarded to the Concentrator. The Concentrator in turncarries out policies dictating which events and scheduled reports mustbe published out to other data center applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate the embodiments of the present inventionand, together with the description, serve to explain the principles ofthe invention.

FIG. 1 is a simplified illustration of the power path from a generationpoint to a distribution substation to a consumer, showing the highvoltage, medium voltage, and low voltage regions of the distributiongrid and depicting some of the major features of an electricaldistribution grid.

FIG. 2a is a simplified fragment of a radial-architecture distributiongrid showing the lack of cycles in the grid topology.

FIG. 2b is a simplified fragment of a looped-architecture distributiongrid depicting two substations each able to deliver power to the servicetransformer delivering low-voltage power to the group of residencesshown. The substation at left is currently powering the residentialgroup.

FIG. 2c is a simplified fragment of a networked architecturedistribution grid. The four feeders shown could originate at a singlesubstation (typical) or at multiple substations. The rectangular gridconnects service transformers peer-to-peer on the low-voltage side sothat all feeders deliver power to the loads below the substationsconcurrently.

FIG. 2d is an exemplary simplified fragment of a campus network. Athree-phase transformer powers a 480 Volt Bus from which depend a numberof three-phase laterals which run through the campus powering individualelectrical outlets. Adding low-voltage generation points to the bus andproviding means to isolate the bus from the distribution line convertsthe campus network into a self-sufficient microgrid.

FIG. 3 is a high-level software deployment model of a Grid LocationAware™ network including back office features, substation apparatus, andtransformer area networks (one expanded) including intelligence atremote hubs and subordinate remotes.

FIG. 4 is a simplified block diagram of the substation apparatus in aGrid Location Aware™ network, illustrating how the Grid Location Aware™network apparatus couples to the existing SCADA lines in the substationand how the data from the Substation Receiver is backhauled to a datacenter.

FIG. 5 is a block diagram of the multi-threaded software architecture inthe Substation Receiver showing how Edge-to-Substation signals areacquired, channelized, detected, demodulated, decoded, and stored forprocessing and backhaul.

FIG. 6 is an elevation of a Remote Hub GLA Smart Meter.

FIG. 7a is a top view of an accurate 3-dimensional model of oneembodiment of the Edge Transmitter module of the Remote Hub GLA SmartMeter for a Form 2S residential meter.

FIG. 7b is a bottom view of the same model of the Edge Transmittermodule.

FIG. 7c is a schematic block diagram of the electronic components of theEdge Transmitter module of the Remote Hub GLA.

FIG. 7d is a detail of the isolation circuit of the Remote Hub.

FIG. 8 is an elevation of a Subordinate Remote GLA Smart Meter.

FIG. 9 is a schematic block diagram of the electronic components of thePLC communication module of a Subordinate Remote.

FIG. 10a is a graph (not to scale) of a snapshot of the AC waveforms ona distribution grid at a meter connection point. The power fundamentaland its odd harmonics are highlighted, and three CDMA-like broadbandfrequency-divided Edge-to-Substation channels are shown, one extendedover time to illustrate time divisions.

FIG. 10b provides a time-domain view of three Edge-to-Substationchannels showing two scheduled and one unscheduled channel.

FIG. 11c illustrates a typical structure of a single Edge-to-Substationmessage burst in one embodiment of the invention.

FIG. 10d illustrates an alternative structure of an Edge-to-Substationmessage burst in another embodiment of the invention.

FIG. 10e illustrates how using multiple chips on the same frequency bandmay prevent collisions.

FIG. 11 illustrates communication paths local to the Transformer AreaNetwork, both within a GLA Smart Meter and between the Remote Hub and aSubordinate Hub. Note that in FIG. 11 the elevations of the Remotesdepict embodiments where a secondary communication module is notemployed.

FIG. 12a illustrates a three-phase service transformer with three TANs.

FIG. 12b illustrates a three-phase service transformer with one TAN andProxy Remotes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises a system and methods for constructingand operating an on-grid data collection network in such a way as tointegrate the network with other adjacent networks and devices presentat the edge, substations, and features of an electrical distributionnetwork, wherein the other networks and devices may include Smart Metersand the AMI and a conventional network such as the Internet. The systemand methods further integrate the data collected by the on-grid datacollection network at a data center and may publish the collected datato other applications. The system and methods may also employ thecapabilities of the integrated networks to infer otherwise unknownstatic and transient attributes of the electrical distribution grid andreport them via the integrated networks for the purpose of improving thephysical and logical network models of the Smart Grid. This leads to theability of the models to support Smart Grid applications such asconservation voltage reduction, volt/Var optimization, load balancing,fault isolation, and recovery management.

FIG. 3 is a logical block diagram of the intelligent platforms of oneembodiment of the invention showing where the different intelligenceresides with respect to a converged network comprising a conventionalwide area network such as the Internet, an Advanced MeteringInfrastructure, the medium voltage electrical distribution grid, and theat least one Transformer Area Network connected at the edge of themedium voltage electrical distribution grid via at least one servicetransformer. FIG. 3 shows that the system may be divided into threeregions or tiers. The edge tier 301 comprises at least one TransformerArea Network (TAN) 302. Each TAN comprises a Service Transformer 303, atleast one Remote Hub 304, and zero or more Subordinate Hubs 305. WhenSubordinate Hubs 305 are present, the Remote Hub communicates with theSubordinate Hubs via a standard short range, PLC protocol, such asPRIME. The Remote Hubs 305 may be operable to transmit current-modulatedsignals. To avoid haying multiple Remote Hubs unintentionally installedon a TAN, the installation procedure may provide a mechanism to allow anewly installed Remote of either type to detect whether Remote Hub isalready present on the local TAN. The invention does not require theinstallation of communication devices or other modifications between theedge tier and the substation tier. However, if it is desirable tocollect data from a feature of the medium-voltage grid such as acapacitor bank, a variation of the Remote Hub device may be installedthere. Such a Remote Hub is technically still at the Edge Tier, since itis powered by a low-voltage outlet located at the feature, and notdirectly from the medium-voltage line(s) upon which the grid feature isinstalled.

Still referring to FIG. 3, the substation tier 306 comprises at leastone Substation Receiver 307 operable to receive transmissions from theRemote Hubs in the edge tier without recourse to any signal amplifiers,bypass mechanisms, or bridges installed on the medium voltageinfrastructure of the electrical distribution grid. The SubstationReceiver(s) connect via a local area network to a Computing Platform 308containing non-volatile computer-readable memory and a CPU for storingand executing the software 309 which maintains the Inventory and GridMap databases and carries out the tasks of provisioning and managing theconverged data network. Additionally the Computing Platform stores andexecutes software 310 which processes the Inventory and Grid Map data incombination with messages received from the Substation Receiver 307 toinfer information about the state of the Grid over and above what theSubstation Receiver alone can detect based only on incomingtransmissions. In some embodiments of the invention, the computer-basedcomponents of the Substation Receiver and the Computing Platformcomponents are hosted on the same server. In such embodiments, thecommunications protocol (such as HTTP) used to transfer data between theSubstation Receiver and the Computing Platform software components neednot change, even though there is no physical local area networkrequired. Computing Platform 308 connects to a conventional wide areanetwork 311, such as the Internet, for the purpose of communicating witha Concentrator 312 in the data center tier 313. In some embodiments ofthe invention, and regardless of whether the Computing Platform andSubstation Receiver are the same server or separate servers, the serversmay be configured in a redundant cluster to ensure continuous operationof the system.

Referring again to FIG. 3, the Concentrator 312 hosts software with ananalogous architecture to the software in the substation(s), comprisinga network and data management component 314 providing software servicesto one or more applications 315 for Grid Location Awareness. Theapplications use conventional network-based messaging protocols such asbut not limited to IMS, SOAP, and REST to publish information tosubscriber applications such as a Geospatial Information System 316. Thedata and network management component 314 may integrate with AMIhead-end 317 for the purpose of causing the AMI network to broadcastdata blocks to the Remote Hubs in the edge tier 301. Data and networkmanagement component 314 may integrate with AMI head end 317 using astandard protocol and/or a proprietary interface defined by the AMIvendor.

Other embodiments of the invention may include the convergence ofalternative ancillary network components. For example,Substation-to-Edge broadcast capability and/or tune synchronization fromthe substations to the Remote Hubs may be provided by medium-voltage PLCtransmitters attached to the feeders at the substation rather than usingan AMI for this purpose. Likewise, a separate radio transmitterbroadcasting messages originating at the substation may be employed. Theradio transmitter does not need to be physically located at thesubstation as long as there is a low-latency network connection from theComputing Platform at the substation to the transmitter. The same radiotransmitter may serve as the Substation-to-Edge channel for amultiplicity of substations. When the Substation-to-Edge channel is notan AMI, synchronization of the Remote Hub clocks may be provided asdescribed in U.S. patent application Ser. No. 13/566,481, titled Systemand Methods for Synchronizing Edge Devices on Channels without CarrierSense, which is incorporated herein by reference. In embodiments of theinvention where channels are not slotted, clock synchronization isunnecessary.

FIG. 4 details how in one embodiment the Substation Receiver 401, hereshown co-hosted on a single server with the other software components ofthe Computing Platform, monitors the feeder lines 402 on the low-voltageside of the substation transformer 403 by attaching secondary currentsensors 404 to the SCADA loops 405 already in place. The secondarycurrent sensors provide inputs to the Substation Receiver. This couplingmethod allows a Substation Receiver to be installed on a substationtransformer without disrupting the operation of the substation. Othercoupling methods such as hot-stick clamp-on current transformers arewell known in the art, and may be equivalently employed in lieu of thesecondary coupling to SCADA loops method described herein. Somesubstations may lack SCADA loops, or they may be inaccessible due tophysical. placement or due to utility regulations.

FIG. 5 details the software architecture and method used by oneembodiment of Substation Receiver logic 501 to capture, detect,differentiate, and decode the multiplicity of signals being receivedfrom the Remote Hubs at the edge of the portion of the distribution gridsupplied by the substation transformer associated with this SubstationReceiver. Inputs from the GLA CT lines 504 arrive at data acquisitionmodule (DAQ) 502 in real-time as raw digitized signals where they arethen buffered and recorded on ramdisk 503. Operating in parallel withthe DAQ process, Channelizer 505 reads the raw signals and reorganizesthem by frequency band of interest into channelized signals stored onramdisk 506. Operating in parallel with the Channelizer, PreambleDetector 507 samples the channelized signals received on everyfeeder-phase attempting to recognize the one or more preamable patternswhich precede every transmission. In one embodiment, the PreambleDetector looks for all legitimate preambles, thereby allowing for thereceipt of transmissions that are outside their allocated time slots orwhich were transmitted on a non-slotted channel. The Preamble Detectormay also use its knowledge of the channel time slots in order tominimize the amount of channelized recordings it must sample. In oneembodiment, when the Preamble Detector finds a preamble, it determinesand marks the point or points in the data stream at which theDemodulator 509 should start processing. Multiple copies of the samemessage may be detected due to crosstalk. All copies are retained fordemodulation. Preamble Detector 507 provides the marker information andChannelized signal data to the Demodulator through ramdisk 508.Operating in parallel with the Preamble Detector, Demodulator 509 readsall copies of the messages from ramdisk 506, uses the frequency bandsand possibly time slots in which the messages were found and the knownpolicies of the Remote Hubs to determine how to decode the message.Policy elements may include the modulation technique in use on thechannel, the time based access policy in use, and, if frequency-spreadmodulation is used, which chips could have been used in modulation.Sometimes there may be more than one possible choice of chip. If thedemodulator attempts to apply the wrong chip, this will be indicated bya demodulation error and/or FEC failure. This parallelized embodiment ofthe receiver logic permits multiple processor cores to operate on eachmessage stream, with the modules early in the data flow operating onlater transmissions, while modules late in the data flow operate onearlier transmissions.

Still referring to FIG. 5, Data Manager 514 may be responsible forsynchronizing the several processes' access to the data stored on theramdisks 503, 506, 508, and 510, so that each process at a given time isoperating on completed data that was output by its predecessor processrather than attempting to access stale or volatile buffers. The DataManager also can copy data from the ramdisks to a large archive disk 513for later study and post-processing. By the time the messages have beendemodulated and written to ramdisk 510, they have been enhanced withenough information to identify the transmitter and infer the feeder andphase on which the message was transmitted, as described in more detailbelow. The message bundle for each feeder-phase on which the message wasreceived may include, but is not limited to, the signal amplitude atcharacteristic frequencies within the frequency band, the signal qualityas determined by Demodulator figure of merit measurements, the time thesignal was received, and the chip, if any, with which the message wasencoded. These message bundles are passed to the Network Management andGrid Location Awareness software via interface 511. These softwarecomponents, not shown in FIG. 5, but shown as 309 and 310 respectivelyin FIG. 3, use the provisioning policies of the edge transmitterstogether with the message properties and the message content todetermine which Remote Hub edge transmitter sent the message, andcompare the signal characteristics of the copies of the message receivedon each different feeder-phase input where it was detectable in order toestablish on which feeder and phase the message was actuallytransmitted. This conclusion is compared with the information in thegrid map to determine if a change in grid topology or state hasoccurred. This allows the Grid Location Awareness algorithm to infer notonly the phase of a meter where the phase was previously unknown, butalso changes in switch states in loop or networked configurations andschematic alterations in any type of grid resulting from repairs andmaintenance.

Referring once again to FIG. 3, the software components 309 and 310 onthe Computing Platform 308 decode the demodulated, error-correctedmessage received from the Substation Receiver at the semantic level. Thesemantic decoding may include decryption and a CRC check on thedecrypted message. This helps preclude the introduction of false data,for example due to tampering with the firmware on the Remote Hubs, orinstallation of a meter from a different service area on the network formalicious purposes. Once the message has passed this level of decoding,the data payload in the message may yield additional grid awarenessinformation. A pairing message indicates that a new meter has beeninstalled successfully, or that a known meter is now connected to adifferent service transformer or a different phase of a multi-phasetransformer. Scheduled data messages may provide information aboutvoltage levels, demand, and power factor at the edge, as well as anyother data or results computed from data available from the instrumentsat the Remotes, limited only by the data-bearing capacity of thechannels. Even the failure of a scheduled message to arrive isinformative, indicating that there may be an outage. Any copy of themessage may be used to extract data, not only the copy from the feederand phase on which the message was determined to have been transmitted.Sometimes the main copy may contain bit errors while crossover copies donot.

When all the information has been extracted from a message bundle at thesubstation, the software components on the Computing Platform apply apolicy to determine what data to forward to the Concentrator 312 viaconventional network 311 for further processing and publication. Inaddition to carrying out data management policies, Computing Platform308 may analyze the archived raw and enhanced signal quality data inorder to determine whether beneficial changes in channel managementought to be made. When such changes are identified, Computing Platform308 may forward recommendations to the Concentrator to ensure that theimpact of all contemplated policy changes is understood at everysubstation that may be affected before the policy is put into effect.

Considering now the devices at the edge of the network, FIG. 6 shows anelevation of a single-phase form 2s GLA Smart Meter 601 which isoperable to act as a Remote Hub in a Grid Location Aware network. Form2s is standard format for a residential single-phase meter in the UnitedStates, Other embodiments of the Remote Hub device may integrate withthree-phase meters, or not be associated with a meter at all, but pluginto a 120V or 240V or other voltage outlet located at a building,especially in a microgrid setting where the edge of the network isdefined with a higher resolution than in a typical utility service area.In still other embodiments, the Remote Hub device may be integrated withother devices and instruments on the distribution grid, such as voltageregulators, capacitor banks, step-down transformers, and the like.

A typical Smart Meter has a layered design of circuit boards conformalto the meter housing, such as a cylindrical transparent dome constructedof glass or Lucite. In the depicted embodiment, the dome may beapproximately 1.5″ taller than usual to accommodate the height of theEdge Transmitter module 604. However, the height of the meter housingvaries from one manufacturer and model to another and does not place themeter in violation of the form standard. Nearest the top of the housingis the Calculation and Display Board 602, which is part of every SmartMeter. Typically, the display features on the Calculation and Displayboard such as indicator lights and a digital readout may be accessed byother components in the housing via interface 606. The Communicationsmodule 603 contains the AMI transceiver circuitry and intelligence. Insome Smart Meters the components of the Communications module 603 arecontained on the Calculation and Display Board, but other smart meterscan accommodate multiple types of Communications Modules by placing thecommunication components on a separate board as shown, Bothconfigurations are common. If on a separate board, Communications Module603 communicates with logic on the Calculation and Display board 602 viaan interface and cable 606. Other types of component-to-componentinterfaces are possible internal to the Smart Meter. The EdgeTransmitter module 604 contains the long-range GLA edge transmitter andalso the short-range PLC transceiver for the TAN communications. Module604 also has a CPU/microcontroller with nonvolatile memory that hostsand executes the stored programs of the Remote Hub control logic,controlling the Edge Transmitter and the PLC transceiver, and theinterface 606 to the other logic boards 602 and 603.

FIGS. 7a, 7b, and 7c show top, bottom, and schematic views of oneembodiment of the Edge Transmitter module. Referring primarily to FIG.7c , the Edge Transmitter Module communicates with other components ofthe meter 701 via UART (Universal Asynchronous Receiver/Transmitter)712. Power is delivered to power supply 703 from AC mains 702. Powersupply 703 provides appropriate low voltage DC power to computing unit717, Amplifier Circuit 705, and Class D Amplifier 707. Computing unit717 is a microcontroller processing unit with on-board volatile andnon-volatile memory, and is used for both short range and long rangedigital signal processing and protocols 704, scaling and filtering 713,and to drive amplifiers 707 and 705. PLC Amplifier Circuit 705 and PLCCoupling Circuit 706 are adjusted so that the medium-frequency signalemitted does not propagate outside the TAN, relying on the servicetransformer's filtering properties at this frequency, as described inmore detail below. The coupling circuit 708 for long range transmissionsis much more powerful, requiring a special isolation circuit 711 whichprevents coupling circuit 708 from resonating with other long-rangetransmissions and grid noise at the frequencies to which it issensitive, when the Remote Hub is not transmitting on a long-rangechannel. The main components of the coupling circuit 708 are transformer709 and capacitor 710. According to some embodiments, the EdgeTransmitter module may contain a GPS receiver, such as GPS receiver 718shown in FIG. 7c . Alternately, the Edge Transmitter module may haveaccess to the GPS signal from a GPS receiver located on anothercomponent of the Remote Hub, such as the Calculation and Display board,or on a mobile computing device used by an Installer. The Remote Hub mayuse the UPS signal to record its geospatial coordinates, and/or forsynchronizing transmissions on a slotted channel so as not to collidewith transmissions from other Remote Hubs. Additionally, a Remote Hubmay be programmed to report its geospatial coordinates, or a function ofits geospatial coordinates, on an Edge-to-Substation channel or topermit them to he read by a mobile computing device.

FIGS. 7a and 7b illustrate how the components of FIG. 7a may be arrangedto conform to the shape of a form 2S electrical meter. As is apparentfrom FIG. 7b , transformer 709 and capacitor 710 may be largecomponents. Shown here removed from the assembly to reveal thetransformer, flux shield 715 normally covers transformer 709 to preventmagnetic flux from the large transformer from interfering with themetrology unit bellow it. Referring to FIG. 7a , the components of PowerSupply 703 occupy a region of the Remote Huh module at the upper left,and the components of Class D amplifier 707 are shown at the upperright. In this embodiment, a single microcontroller 717 containscircuitry, a processor, and nonvolatile memory for firmware protocolstacks and network management logic 704, 705, and 713 (from FIG. 7c ).The large components at the lower right are PLC coupling circuit 706,isolation circuit 711, and an amplifier capacitor 716 for the long-rangeedge transmitter. Connector 712 is the connector for interfacing withthe other logic boards in the meter housing.

FIG. 7d details the isolation circuit 711. This circuit provides theability to disconnect the coupling circuit of the Edge-to-Substationtransmitter from the power line. It is desirable that the Remote Hub beisolated from the power line except when it is transmitting. This isbecause the coupling circuit represents a substantial load whenconnected to the power line. The isolation circuit consists of a Triac718 and a relay 719. The purpose of the Triac is to allow connecting tothe power line at the time of a zero crossing of the line voltage. Thisprevents the generation of large transients that can damage componentsin the Remote Hub. Additionally, making the connection with the Triacremoves the concern of arcing on the relay contacts that reduces thelife of the relay. The sequence of events when a Remote Hub interactswith the power line is:

a. The Triac is closed at a zero crossing of the power lineb. The relay is closedc. The desired action (generally a transmission) is performedd. The relay is openede. The Triac is opened at a zero crossing of the power line.

FIG. 8 is an elevation of a standard Smart Meter 801 with a standardCalculation and Display Board 802 and a standard metrology unit 804.Meter 801 becomes a Subordinate Remote GLA Smart Meter with the additionof PLC communication capabilities on the Communications Module 803. ThePLC communications components are small enough that they can share spaceon module 803 with the AMI communications circuitry if preferred. Allthree modules (if three are present) communicate via an interface, here,a serial interface or UART 805. Other embodiments may employ adifferent, functionally equivalent internal inter-component interface.

FIG. 9 is a schematic diagram of the PLC communications components onthe Communications Module of one embodiment of a Subordinate Remote. Byanalogy with similar components on the Edge Transmitter Model in FIG. 7c, the communications module of a Subordinate Remote comprises the basicmeter 901, power input from AC mains 902, interface to the basic meter907, power supply 903, microcontroller unit 904, amplifier circuit 905,and PLC coupling circuit 906. The transmitter may be tuned to ensurethat the signals are sufficiently attenuated by the service transformernot to be received above the service transformer or below adjacentservice transformers. A Subordinate Remote may also contain a GPSreceiver. Alternately, a Subordinate Remote may be programmed with itsgeospatial coordinates by means of a GPS receiver in a mobile deviceused by an Installer. A Subordinate Remote which knows its geospatialcoordinates may report them over a Transformer Area Network to a RemoteHub. This allows the Remote Hub to compute extended geospatialinformation such as the area and extent of the TAN. The Remote Hub mayreport this extended geospatial information on an Edge-to-Substationchannel or the information may be read from the Remote Huh by a mobiledevice used by an Installer or other field engineer.

FIG. 10a illustrates both the characteristics of the low end of thefrequency spectrum on a feeder-phase line of a typical distribution gridand the method employed by a Remote Hub's Edge Transmitter to injectcurrent modulated signals onto the grid in such a way to allow all theTANs served by one substation transformer to be able to transmitscheduled Grid Location Awareness reports at least twice in each 24 hourperiod, and to additionally transmit alerts as necessary, withoutcreating any of the difficulties described herein above which have beenobserved with prior art methods of on-grid transmissions. Importantcharacteristics of the spectrum are the 50 Hz or 60 Hz power fundamental1001, its harmonics 1002, and the noise floor 1003. It should be notedthat from time to time a spike of impulse noise may exceed the usualnoise floor. The defined channel or channels for modulated signalstransmitted by an Edge Transmitter occupy a broad candidate spectrumlying between the 50 or 60 Hz power fundamental and the low-passthreshold of the service transmitters on the host power grid. Thecandidate spectrum for a particular substation is determined bymeasurement and set by policy and subject to regulatory constraints.Measurements determine which band or bands of the candidate spectrum arereliably received at each substation transformer. If a usable band iswider than the bandwidth needed for a reliable transmission, then thechannel band may be defined to be variable. In such cases, the RemoteHub conducts measurements, described herein below, prior to transmittingto determine at present conditions which part of the wider channel iscurrently most favorable for transmitting. Conversely, at the SubstationReceiver, the preamble detector samples the entire wide usable band,determining the actual band used by the transmitter based on where thepreamble was detected.

FIG. 10a shows three frequency bands 1004, 1005, and 1006 which havebeen defined as channels for the long range Edge Transmitters The numberof bands used as channels is not limited to three, nor are threechannels always required. Transmissions on each channel are spreadacross a defined frequency band as shown using a broadband modulationtechnique such as the ones identified herein above. Additionally,transmission bursts may be constrained to occur in time slots such as1007. Details of the slotting protocols are explained herein below.

Still referring to FIG. 10a , a typical frequency based channel of thepresent invention may span a wide enough area of the spectrum thatseveral harmonics of the power fundamental occur within the channel.Because it is important to keep the amplitude of the injected, modulatedcurrent as near as possible to the noise floor and to minimize theamount of power used to transmit, in some embodiments of the presentinvention no signal is added to the spectrum at harmonics of the powerfundamental. A shaping filter may be beneficially applied by the EdgeTransmitter to avoid injecting current over the harmonics. Thistechnique is also beneficial at the Substation Receiver, which may applycomb filtering so that the preamble detector and demodulator are notrequired to process the signal on the harmonics. This saves valuableprocessor capacity in the compute-intensive demodulation process.

When the modulation technique used is frequency spreading, eachfrequency band (such as 1004, 1005, and 1006) which is used as a channelis assigned at least one patterned code, or chip. The rate of frequencyvariation of the chip is much higher than the rate of variation of thedata signal. The actual frequency-spread transmission injected ascurrent on the channel is the exclusive or (XOR) of the channel's chipand the data signal. Adjacent and nearby channels are assignedmathematically orthogonal chips. The amplitude of the frequency spreadcurrent signals is as close as possible to the noise floor of the powerline. This is beneficial in eliminating the problems associated withprior art PLC methods. For example, if a transmission on one channel is“folded over” into another channel due to crosstalk, the differentencoding chips used causes the receiver to interpret the “stray” signalas noise, allowing the receiver to still extract the correct signal.Additionally, and regardless of the modulation technique, any harmonicsfrom one channel which extend into adjacent channels will also beinterpreted as noise. The result of this combination of channel accessrestrictions and modulation techniques is one or more low-frequency,high-quality current-modulated channels which can bear (in individualbursts) a raw data rate of 120 bits per second or more, or, by example,80 bps after forward error correction, using interleaving techniques todistribute data bits and FEC bits to minimize the probability of loss ofrelated bits due to impulse noise. Time-duration testing on a radialdistribution grid, transmitting an average distance of 3.5 miles line ofsight from the substation, yielded a frame error rate of 1.6e-6 using anEEC rate of ⅔ with frequency spread modulation. It is recognized thatthe method and apparatus described may additionally be operated at lowerdata rates than cited.

FIG. 10b illustrates one method of organizing a group of three reliablechannels to support grid mapping. All three channels are organized intotime slots 1007, within which Remote Hubs are provisioned to transmitaround a 5-second burst 1008 with around 1 second of silence prior tothe burst and around 1 second of silence after the burst. This yields aninter-burst interval 1009 averaging 2 seconds long. Different timeintervals may also be used. The reason for the long inter-burst intervalin the illustrated embodiment is that the mechanism for synchronizingthe transmitter clocks may be an AMI network, and the AMIsynchronization mechanism, being typically based on a mesh or cellularwireless architecture, is no more precise than plus or minus one second.Collisions (overlapping transmissions) on the same channel must beprevented because they will destructively interfere with one another ifthey were modulated using phase-shift keying or the same chip. In oneembodiment of the invention, each data-bearing frequency-spread channelis assigned a plurality of chips instead of one. For example, if thenumber of chips per channel is two, then transmissions on even-numberedtime slots use one chip, and transmissions on odd-numbered time slotsuse another, mathematically orthogonal chip. Using multiple chips mayallow data-bearing capacity of the channel to be increased by reducingthe inter-burst interval, as overlaps of adjacent transmissions maystill be decoded. The ordinal number of a time slot is determined withrespect to a Master Frame Origin, which may be defined as beginning atmidnight local time of each day, or may be established by a variety ofmethods as described in U.S. patent application Ser. No. 13/566,481already referenced and incorporated herein.

Two of the channels 1011 in FIG. 10b have a scheduled organization. Thismeans that each Remote Hub is assigned specific time slots in which itmay transmit on the channel. A third channel 1012 is still organizedinto slots, but any Remote Hub with an exceptional condition to reportmay attempt to transmit in any time slot, provided that it has notalerted recently. Specifically, channel 1012 is organized by the methodknown as slotted aloha. Alerts, when received at the substation, aretypically acknowledged via a Substation-to-Edge channel such as awireless AMI network. If available, other methods for acknowledgingalerts may be employed. If no mechanism for acknowledging alerts isavailable, then each alert can simply be transmitted multiple times,with a randomly selected number of slots having elapsed between thetransmissions. This, however, reduces the data bearing capacity of thealerting channel 1012, because in standard slotted aloha, alerts areretransmitted only if they are not acknowledged. The rate of messagefailure will be the frame error rate of the channel (already disclosedto be very low) plus the rate of collisions. The rate of collisions inturn depends on the offered load, which is based on the probability thatmore than one Remote Hub will attempt to transmit in a given slot. Theoptimum number of unacknowledged retransmissions to maximize messagesuccess rate is likely to be a small number such as two or three,because with higher transmission rates channel saturation may occur.

The organization of an unscheduled channel may also use an un-slottedprotocol similar to pure aloha, wherein the channel is not divided intotime slots, but wherein a transmitter may attempt to transmit at anytime, given that it has not already transmitted within a predefinedrecent interval. In this organization, alerts may preferably beretransmitted only if not acknowledged within a predetermined period ofelapsed time, or they may routinely be transmitted a multiplicity oftimes if acknowledging alerts is impossible or undesirable.

The number and organization of channels described is by example only. Onsome substations, only one reliable channel may be available. When onlyone channel is used, either because of conditions or by design, aplurality of time slots may be reserved for alerting, while other timeslots are scheduled. On some substations, a plurality of reliablechannels will be identifiable. The number of scheduled channels neededdepends on the number of Remote Hubs and the number of scheduledmessages each Remote Hub must send in a 24-hour period. In oneembodiment, two channels are sufficient to permit 12,000 hubs totransmit twice daily. If (as is usual) the substation transformersupplies many fewer than 12,000 hubs, fewer channels than are availableare required for scheduled messages, alert thresholds may be lowered,and more than one channel may be dedicated to alerts to accommodate thehigher offered load. FIG. 10b shows four alerts transmitted in the timeinterval shown. Two of the alerts 1010 have a high probability of beingdetected at the substation receiver. The alerts 1013 have collided inFIG. 10b and will not be received correctly. FIG. 10 e, conversely,illustrates how the use of chips selected by means of the modulus of thetime slot prevents some collisions. Here, because of poorsynchronization of docks, message 1014, transmitted in an even-numberedslot of random slotted channel 1012, has overlapped with message 1015,transmitted on the same channel in the subsequent odd-numbered slot.Both messages are decipherable at the substation because they wereencoded using orthogonal chips. This is in contrast with the situationin FIG. 10 b, where the intent of the two transmitters of messages 1013was clearly to attempt to transmit in the same slot. These messageswould still collide even if multiple chips were in use. In yet anotherembodiment of the invention, an unscheduled, unslotted channel might usefrequency spread modulation and be assigned a plurality of orthogonalchips. A transmitter offering a message would select a chip from theplurality of chips at random, thereby reducing the probability that themessage would collide with another transmission on the same channel atan overlapping time.

FIG. 10c illustrates the detailed organization of a typical singletransmission burst, whether it occurs on a scheduled channel or aslotted alerting channel according to one embodiment. Within Time Slot1007 and burst 1008, the message is comprised of preamble 1014,interleaved data bits 1015 and FEC bits 1016. The preamble is the samefor all messages on the channel. The FEC rate is not drawn to scale, andmay be varied as needed from substation to substation based on thequality of the available channels. In some grid locations and/or withsome modulations, FEC may not be required. FIG. 10c without furtherelaboration may appear to imply that the bandwidth is the same for alltransmissions in the same channel, and that the pattern used forpreamble detection is also suitable for use by a Substation Receiverwhen sampling and comparing signals on several inputs representingdifferent phases of different feeders to infer the line on which thesignal was actually transmitted. Some embodiments of the invention mayrequire greater bandwidth for preamble detection than the data-bearingsegment of a message requires. Additionally, in some embodiments, thegrid location of a Remote Hub transmitter may be better inferred from aspecial transmission, called a probe transmission, again measured at thesubstation on all phases of all feeders monitored by a SubstationReceiver. The probe transmission may consist of known modulated signal,or it may consist of pure tones. The pure tones may be transmitted as asequence of single tones, or one or more groups of pure tones may betransmitted simultaneously. The frequency range of the probetransmission may be different from that of the other message sections.FIG. 10d illustrates this bandwidth variation, showing one bandwidth forthe preamble 1018, another bandwidth for data-bearing message 1019, anda third bandwidth for GLA trailer 1020. GLA trailer 1020 is not presentin all embodiments of the invention, because the probe transmission maybe present within preamble 1018. In another embodiment, the probetransmission may precede the preamble rather than following the message.Generally, the segments of a message may be transmitted in any order aslong as the order is known by the receiver.

FIG. 11 shows a Remote Hub 1101 and a Subordinate Remote 1102illustrating the local communication paths within a TAN according to oneaspect of the invention. This figure shows an embodiment where theCommunications Module is not separate from the Calculation and DisplayModule. The Remote Hub 1101 may poll each known Subordinate Remote, viaa PLC protocol such as PRIME or G3 using request path 1103. (To allowfor the use of different PLC protocols, the specific language of thesestandards is not used herein. By way of example, if the. PLC protocol inan embodiment of the invention were PRIME, then the Remote Hub would bea PRIME base node and all other nodes would be service nodes.) A polledSubordinate Remote 1102 retrieves the requested data from the SmartMeter and formats it into a response which is transmitted as a response1104. The Remote Hub's Edge Transmitter Module communicates with theCommunications Module and Calculation and Display Board components viaUART 1107, using a simple request/response protocol 1105 which may varyfrom one Smart Meter vendor to another. Data path 1106 illustrates thatboth the Remote Hub and the Subordinate Remote are members of the AMIand will be transmitting meter data to the AMI head end in addition toperforming TAN-related activities. The Remote Hub, in its role as TANmanager, may make use of the AMI or other alternative, integratedchannels in ways that Subordinate Remotes may not. Only the Remote Hubis capable of sending out messages on the Edge-to-Substation channel. ARemote Hub may also send messages on alternative, integrated outgoingchannels such as the AMI. The Remote Hub may additionally receive datablocks from a Substation-to-Edge channel, whether the Substation-to-Edgechannel is provided by the AMI or other means. Such data blocks maycontain, but are not limited to, alert acknowledgements, firmware updatebroadcasts, and policy changes. Meter clock synchronization messages arepart of the native AMI protocol, but the Remote Hub may obtain thesynchronized clock time from the Calculation and Display module when anAMI is present.

Remote Hub 1101 has the capability to function in multiple operatingmodes. The Remote Hub may function as a Subordinate Remote. The RemoteHub may also function as a hybrid of Remote Hub and Subordinate Remote,called a Proxy Hub. When a Remote Hub 1101 is first installed, itmonitors the PLC frequencies on the TAN for a period of time sufficientto determine whether another Remote Hub is already present. The waittime consists of a fixed period of time plus an additional period oftime computed by a randomization function when the device is powered on.The fixed period of time is sufficient to ensure that a Remote Huboperating in the master mode would have executed its discoveryalgorithm, which would be detected by the newly installed Remote Hub ifanother Remote Hub is operating within range. Typically, “within range”means powered by the same service transformer, but exceptions occur. Themeans of handling the exceptions are described herein below.

If a first Remote Hub is already present, Remote Hub 1101 indicates bymeans of a light or digital display on the face of the Smart Meter thatanother Remote Hub is present. At this point, an installer may elect toleave redundant Remote Hub 1101 in place, or replace it with aSubordinate Remote unit. If left in place as a “spare,” Remote Hub 1101continues to function as a Subordinate Remote, and the first Remote Hubcontinues to act as the Remote Hub and master node in the TAN. If noother Remote Hub is present, Remote Hub 1101 begins to operate as amaster PLC node on the TAN, discovering and storing a list of anySubordinate Remotes 1102 in the same TAN. A Remote Hub may also enter athird mode, Proxy Hub, as described below. As soon as it takes on themaster or hub role, Remote Hub 1101 obtains the network system time ifavailable, for example by querying the AMI logic in the Smart Meter, andformats, encodes, and transmits a provisioning request on anEdge-to-Substation channel reserved for provisioning requests andalerts. When a Substation Receiver detects the provisioning request, itmay cause a provisioning response to be sent, either via the AMI, or viaan available on-grid or wireless Substation-to-Edge channel.Provisioning data may also be supplied to a Remote Hub by means of ahandheld device or drive-by transmitter employed by the installer. Thehandheld device uses a personal-area wired or wireless protocol, such asBluetooth, infrared, USB, or RS232 to program the Remote Hub. Inembodiments of the invention where the Substation-to-Edge channel isabsent or very constrained, the Remote Hub may be provisioned viahandheld without knowledge of the inferred grid location of the RemoteHub. The same short-range protocol, in a handheld or drive-by device,may be used to distribute firmware or policy updates to Remote Hubs thatlack a permanent Substation-to-Edge channel. It is sometimes desirableto activate a policy or program change simultaneously on a collection ofRemote Hubs. If the Remote Hubs must be updated by means of apersonal-area protocol, the programming device converts the desiredfuture activation time to a relative wait time as each Remote Hub isprogrammed, so that even though the Remote Hubs were programmed atdifferent times, they will activate the updated programming atapproximately the same future time. Remote Hubs may be manufactured witha default policy, or pre-loaded with a default policy aftermanufacturing but before installation, so that if no policy is providedat or subsequent to installation, the Remote Hub still has a rule foroperating.

The provisioning data provides the Remote Hub with the information itneeds to manage the TAN, including the location of, and organization of,other channels on the Edge-to-Substation network, and the ordinal orsequence number of slots on scheduled channels on which this Remote Hubhas permission to transmit. When the Remote Hub discovers SubordinateRemotes, it transmits pairing messages on the Edge-to-Substation channelto inform the Computing Platform that it is in communication with thenewly discovered Subordinate Remotes. Pairing messages may betransmitted on an alerting channel or on a scheduled channel dependingon a policy established by the network. When a Remote Hub acting in themaster role has discovered another Remote Hub on the same transformerand phase operating in the subordinate role, the resulting pairingmessage indicates this. Including the presence of “spare” Remote Hubs inthe Grid Map may provide a cost savings and more rapid recovery, in thatif the master Remote Hub should fail, the TAN may be reconstructed byallowing the spare Remote Hub to assume the master role. The masterRemote Hub may cache its policy information on a spare Remote Hub, ifpresent, in order to allow the failover to occur even withoutre-provisioning the TAN.

Hereinafter are disclosed methods for properly partitioning Remotedevices into TAN groupings. PLC transmission power is controlled inorder to keep the signal that gets through the Service Transformer lowenough to avoid interference with other TANs. Specifically, unlessspecial accommodations in configuration are made as described hereinbelow, a Remote Hub must poll and collect data from only SubordinateRemotes on the same phase of the same service transformer as the RemoteHub. However, at certain sites on some grids, it may happen that at PLCstandard power and frequencies, the PLC transceivers in the Remotes maybe able to discover Subordinate Remotes and Remote Hubs on other phasesof the same service transformer, or even on adjacent or nearby servicetransformers. In this aspect of the invention, the detectable remotesmay be partitioned wherever possible so that each TAN comprises exactlyone master Remote Hub and all Subordinate Remotes, or Remote Hubs actingas Subordinate Remotes, on the same phase of the same servicetransformer, and no Remotes of any type which are on a different phaseor a different service transformer.

In one embodiment of the invention, a Remote Hub's PLC protocol stackexecutes its discovery process, which involves transmitting a beacontone or message that causes other nodes in the vicinity to respond. Thefirst time this is executed, a standard initial power level is used. TheTAN management layer of the Remote Hub, operating above the PLC protocolstack, obtains the list of discovered Remotes of any type. The EdgeTransmitter of the Remote Hub is then employed to send a pilot signal atsufficiently low amplitude and high frequency that the pilot signal willnot be detectable on the high-voltage side of the service transformer.(This pilot tone is not the same as a PLC discovery beacon.) The pilotsignal begins on a zero crossing of the power fundamental of the phaseon which the transmitter resides. Other Remotes (of any type) whichdetect the pilot signal test to determine if the received signal beganon the zero crossing of the phase on which the receiving Remote resides.If so, the receiving Remote sends a positive response on the PLC channeland records the identity of the Hub Remote that sent the pilot tone.Another Remote Hub on the same phase as the pilot transmitter entersSubordinate Remote mode and will be considered a spare. SubordinateRemotes on other phases do not respond to the pilot tone. A Remote Hubthat detects the pilot tone but is on a different phase sends a negativeresponse. The transmitting Remote Hub uses the responses to update itsinventory of TAN devices discovered automatically by the PLC discoveryprocess, recording the list of Subordinate Remotes and spares on itshome phase, and the list of Remote Hubs on other phases of the sameservice transformer. Remote Hubs which sent neither a negative nor apositive response are presumed to be on another service transformer. Ifthis case exists, the value of the “initial” power level (amplitude) forthe PLC discovery beacon is reduced, so that next time the fulldiscovery process is executed, it will be less likely that any Remoteson other service transformers will respond.

Next, the first Remote Hub that transmitted the pilot tone examines thelist of negative responders, that is, of Remote Hubs on a differentphase. It selects one such second Remote Hub and orders it via the PLCprotocol to transmit a pilot tone of its own. The first Remote Hub,still the master node of at least all the nodes on the servicetransformer, collects the resulting positive and negative responses andupdates its inventory and partitioning data. At this point, any spareRemote Hubs on the same phase as the second Remote Hub have also enteredSubordinate Remote mode, and the first Remote Hub now has a completepartitioning of Remote Hubs according to phases, the Remote Hubs on thethird phase, if present, being the intersection of the Remote Hubssending negative responses to the first Remote Hub with the Remote Hubssending negative responses to the second Remote Hub.

If a third phase is present, the first Remote Hub now selects a thirdRemote Hub from the third phase, and orders it via the PLC protocol totransmit a pilot tone and return the list of negative and positiveresponses it received. At this point, a positive response will have beenreceived from every Subordinate Remote on the service transformer, thephase and mode of every device on the service transformer is known, anda potential master Remote Hub for each single-phase TAN has beenidentified. Additionally, any node which responded to the original PLCdiscovery process from outside the transformer area has been identified.

Now the first Remote Hub sets its PLC transmission amplitude to a verylow level and polls each remote. This first amplitude should be so lowthat no remotes respond. The first Remote Hub increases its transmissionamplitude until, ideally, all remotes on the same phase and no remoteson another phase respond. The first Remote Hub records this lowthreshold level and then continues to increase the amplitude until aremote on another phase responds. The first Remote Hub records this asits high threshold level.

Now the first Remote Hub commands the second Remote Hub via PLC toattempt to take on the role of PLC master node for its phase, sending inthe command the low and high threshold amplitudes. This is called thepartitioning command. The second Remote Hub sets the PLC transmissionamplitude to the low threshold amplitude, and restarts its PLC stack asa master node, conducting a PLC discovery process of its own. If thesecond Remote Hub discovers all the Subordinate Remotes and spares onits own phase and no nodes on any other phase, then has become themaster of a single-phase TAN and the partitioning step has succeeded.Otherwise, it raises its PLC transmission amplitude and repeats theprocess until the partitioning step succeeds. If the second Remote Hubreaches the High Threshold amplitude without having discovered all theRemotes on its phase, or if at any amplitude a Remote from a differentphase is discovered when no lower amplitude discovers all the Remotes onthe same phase, then the partitioning command has failed. The secondRemote Hub signals the failure of the partitioning command to the firstRemote Hub by using its Edge Transmitter to transmit a status beacondetectable by the First Remote Hub, since the first and second RemoteHubs can no longer communicate via PLC.

If the first Remote Hub detects no failure beacon from the second RemoteHub, and a third phase is present, the first Remote Hub sends apartitioning command to the third Remote Hub, which carries out thepartitioning step as described.

When the first Remote Hub has partitioned the other phases presentwithout having received a failure beacon, then it carries out thepartitioning step itself. If the first Remote Hub's partitioning stepsucceeds, then the service transformer is successfully partitioned intothree single-phase TANs, as shown in FIG. 12a . In another embodiment ofthe invention, the second and third Remote Hubs may employ a failurebeacon and a success beacon. Use of the success beacon may shorten thetime required to complete the partitioning steps.

Referring now to FIG. 12a , which is a simplified schematic drawing of athree-phase service transformer and the meters that it supplies withpower. This service area contains three TANs 1204, 1205, and 1206, onefor each phase of the service transformer. Each TAN contains a RemoteHub 1202 and zero or more Subordinate Remotes 1203. Any SubordinateRemote may actually be a spare Remote Hub. FIG. 12a illustrates a properpartitioning of the Remotes powered by a three-phase transformerfollowing the discovery and partitioning algorithm described hereinabove.

As is clear from the above description of a discovery and partitioningalgorithm, it is possible that for some multi-phase transformers thereis no set of PLC transmission frequencies that will yield a cleanpartitioning of the Remotes on the service transformer into single-phaseTANs. When the partitioning algorithm fails at any step, the firstRemote Hub attempts to form a multi-phase TAN which includes all Remoteson all phases of the service transformer, but no Remotes which are noton the service transformer. Refer now to FIG. 12b , which illustrates amulti-phase TAN. Recall that the first Remote Hub already has aninventory of all Remotes on any phase of the service transformer, andthat it further is aware which node on each phase are Remote Hubs.Beginning with the previously recorded “initial” PLC transmissionamplitude, the first Remote Hub initiates a PLC discovery process. Ifany Remotes are discovered which are on a different service transformer,the first Remote Hub lowers the PLC transmission amplitude, supersedingthe old value of the “initial” amplitude, and restarts the discoveryprocess, repeating this until all and only the Remotes known to be onthe service transformer are discovered. If a new Remote never beforedetected is found, the pilot beacon method above is used to determinethe phase of the new Remote and whether it is on the same servicetransformer as the first Remote. If no transmission amplitude can befound that discovers all and only Remotes on the same servicetransformer as the first Remote Hub, the first Remote Hub transmits adistress alert on an Edge-to-Substation channel and organizes the TAN atthe highest amplitude which does not discover any nodes outside theservice transformer, even if some nodes on the service transformer areunresponsive.

For Grid Location Awareness and the energy management applications thatdepend on the Grid Map to be effective, probe transmissions mustoriginate from each phase of the Service Transformer. To accomplishthis, the first Remote Hub, Master 1202 in FIG. 12b , sends commands tothe second (and third, if present) Remote Hubs 1208, causing them tooperate as Proxy Hubs. A Proxy Hub behaves like a Subordinate Remote onthe TAN, except that it is responsive to certain commands from itsmaster Remote Hub that allow the Remote Hub to control the Proxy Hub'sEdge Transmitter. Remote Hub 1202 stores the Edge-to-Substationprovisioning policies that would normally be carried out by the ProxyHubs 1208. Remote Hub 1202 carries out all the TAN managementactivities, such as polling the Subordinate Remotes, distributingupdates, and computing derived results, for the Remotes, including ProxyHubs, on all phases present. When it is time for a Proxy Hub to send anEdge-to-Substation transmission, the first Remote Hub 1202 formats theappropriate message and sends it to the Proxy Hub over the TAN. TheProxy Hub then retransmits the message on the Edge-to-Substationchannel. In this way, Edge-to-Substation transmissions are alwaystransmitted on the correct phase, even though the TAN master is on adifferent phase.

The partitioning and discovery methods disclosed above are designed toaccommodate a standards-based PLC protocol stack such as PRIME. Use ofalternative short-range PLC protocol stacks may require minormodifications to the methods. More straightforward methods may also beused in cases where customizations to the lower layers of the protocolstack are allowable.

Another aspect of a Remote Hub's channel management capability is thatthe Remote-hub may pre-modulate and store certain messages which do notcontain variable data and may be sent repeatedly. Examples ofpre-recordable messages include messages sent on the provisioningchannel, such as the provisioning request and standard alerts onconditions such as sags, over-voltages, and the like. This strategysaves computing power at the Remote Hub. When policy changes such aschanges in chip, channel placement, baud rate, FEC rate, and bandwidthoccur, pre-modulated recordings may need to be discarded andre-computed. This may be done during idle periods when the EdgeTransmitter's microcontroller CPU is not busy with preparing scheduledmessages. To accommodate this, such policy changes may be announced inadvance to take effect at a known future time as opposed to becomingeffective immediately.

In some embodiments a Remote Hub may not be integrated into a GLA SmartMeter, but instead may be associated with another feature of a mediumvoltage distribution grid, such as a capacitor bank, step-downtransformer, voltage regulator, storage battery, local generator, orswitch set. The Remote Huh may be integrated with local or remotelycontrolled SCADA systems associated with the feature. The SCADA systemmay provide an Edge-to-Substation channel for provisioning Remote Hubsused in this manner, or the Edge-to-Substation channel associated withRemote Hubs in Smart Meters may also be operable to communicate withsuch feature-based Remote Hubs. Such Remote Hubs may incorporate aversion of a Substation Receiver and be operable to send PairingMessages associating the grid feature with other Remote Hubselectrically and schematically subordinate to the grid feature. A RemoteHub may also be embodied as a standalone device plugged into anelectrical outlet. A form of Substation Receiver may additionally beassociated with such medium voltage grid features, or any intermediatepoint on the medium voltage distribution grid. Such an intermediateReceiver may collect information regarding which Transformer AreaNetworks are impacted by an associated medium-voltage grid feature. Thecombination of such a secondary Receiver and Remote Hub may be employedto control intermediate grid features, such as using a switch or relayto isolate a microgrid or balance the load on a plurality ofsubstations, or to alter the set-point on a voltage regulator.

In a further aspect of the invention, a Remote Hub may carry out linemeasurements to determine locally optimum conditions for transmitting.The Remote Hub always has the option to vary the amplitude of theinjected signal, and may additionally have the option to vary thefrequency band of the data bearing segment of the transmission.

To conduct the measurements, the Remote Hub transmits a sequence orsimultaneous combination of pure tones. These tones may be independentof an actual message transmission, or they may be incorporated in themessage preamble. Recall that the bandwidth of the preamble may bedifferent than the bandwidth of the data-bearing segment of thetransmission. If there is an opportunity to choose the frequency band ofthe data bearing segment, then the tones must span the entire availablespectrum. When the tones are transmitted, the current generated at therequested voltage is measured. The relationship between the requestedvoltage and the generated current is calculated at each frequency. Theresult will be proportional to the line impedance of the grid at theRemote Huh for each frequency. This allows the Remote Hub to determineboth how much drive voltage is required to generate the desired currentat each frequency in the available frequency band, and, if there is achoice of frequency bands to use, to select the frequency range thatrequires the least voltage to achieve the desired current, In someembodiments where a Substation-to-Edge channel is available and hassufficient capacity, the Computing Platform may from time to time sendfeedback from the Substation Receiver about the messages as received.This may allow the Remote Hub to refine and calibrate its measurementprocess. Outcomes of this feedback may include changing the slotassignments and/or modulation methods of individual Remote Hubs and/oran entire channel to improve message success rate.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Obviously many modifications and variations are possible in light of theabove teaching. The embodiments were chosen and described in order tobest explain the principles of the invention and its practicalapplication to thereby enable others skilled in the art to best utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the claims appended hereto.

What is claimed is:
 1. A method comprising: determining, by a remote hubcomprising a processor device, a frequency band from a candidatespectrum available on an electrical distribution grid to which theremote hub is coupled on a low voltage side of a transformer; obtaining,by the remote hub, a data payload; creating a message based on the datapayload that includes information in the message to facilitate detectionof the message and inference of a grid location of the remote hub; andtransmitting, by the remote hub to a substation receiver coupled to theelectrical distribution grid on a high voltage side of the transformer,the message onto the electrical distribution grid via a modulatedcurrent signal.
 2. The method of claim 1 wherein the message comprises apreamble, the data payload, and a probe transmission configured toestablish the grid location of the remote hub.
 3. The method of claim 2wherein the preamble comprises the probe transmission.
 4. The method ofclaim 2 wherein the probe transmission comprises a sequence of at leastone sweeping group comprising at least one tone.
 5. The method of claim1 wherein creating the message further comprises identifying, in themessage, a newly discovered remote hub that is subordinate to the remotehub, the newly discovered remote hub being coupled to a same phase ofthe electrical distribution grid as the remote hub.
 6. The method ofclaim 5 further comprising: receiving, by the remote hub from the newlydiscovered remote hub, data that quantifies a measurement taken by thenewly discovered remote hub; and wherein creating the message furthercomprises identifying, in the message, the data that quantifies themeasurement taken by the newly discovered remote hub.
 7. The method ofclaim 1 wherein transmitting the message onto the electricaldistribution grid via the modulated current signal further comprisestransmitting the message onto the electrical distribution grid via themodulated current signal at a zero crossing of a power fundamental of aphase of the electrical distribution grid to which the remote hub iscoupled.
 8. The method of claim 1 wherein determining the frequency bandfrom the candidate spectrum available on the electrical distributiongrid to which the remote hub is coupled further comprises receiving,from a substation transmitter coupled to the electrical distributiongrid on the high voltage side of the transformer, information thatidentifies the frequency band.
 9. A remote hub comprising: a memory; anda processor device coupled to the memory and configured to: determine afrequency band from a candidate spectrum available on an electricaldistribution grid to which the remote hub is coupled on a low voltageside of a transformer; obtain a data payload; create a message based onthe data payload that includes information in the message to facilitatedetection of the message and inference of a grid location of the remotehub; and transmit, to a substation receiver coupled to the electricaldistribution grid on a high voltage side of the transformer, the messageonto the electrical distribution grid via a modulated current signal.10. The remote hub of claim 9 wherein the message comprises a preamble,the data payload, and a probe transmission configured to establish thegrid location of the remote hub.
 11. The remote hub of claim 10 whereinthe preamble comprises the probe transmission.
 12. The remote hub ofclaim 10 wherein the probe transmission comprises a sequence of at leastone sweeping group comprising at least one tone.
 13. The remote hub ofclaim 9 wherein to create the message the processor device is furtherconfigured to identify, in the message, a newly discovered remote hubthat is subordinate to the remote hub, the newly discovered remote hubbeing coupled to a same phase of the electrical distribution grid as theremote hub.
 14. The remote hub of claim 13 wherein the processor deviceis further configured to: receive, from the newly discovered remote hub,data that quantifies a measurement taken by the newly discovered remotehub; and wherein to create the message the processor device is furtherconfigured to identify, in the message, the data that quantifies themeasurement taken by the newly discovered remote hub.
 15. The remote hubof claim 9 wherein to transmit the message onto the electricaldistribution grid via the modulated current signal the processor deviceis further configured to transmit the message onto the electricaldistribution grid via the modulated current signal at a zero crossing ofa power fundamental of a phase of the electrical distribution grid towhich the remote hub is coupled.
 16. The remote hub of claim 9 whereinto determine the frequency band from the candidate spectrum available onthe electrical distribution grid to which the remote hub is coupled, theprocessor device is further configured to receive, from a substationtransmitter coupled to the electrical distribution grid on the highvoltage side of the transformer, information that identifies thefrequency band.